1. Field of the Invention
This invention relates to the manufacture of integrated circuits, and more particularly to wafer fabrication systems including measurement systems for measuring characteristics of integrated circuit structures.
2. Description of Related Art
Integrated circuits are typically formed by processing one or more semiconductor wafers as a xe2x80x9clotxe2x80x9d through a series of wafer fabrication tools. Each wafer fabrication tool typically performs a single wafer fabrication operation upon the semiconductor wafers of the lot. For example, a given tool may perform a layering operation, a patterning operation, a doping operation, or a heat treatment upon the semiconductor wafers. A layering operation may add a layer of a desired material to an exposed surface of the semiconductor wafers. Common layering operations include thermal oxidation, chemical vapor deposition (CVD), evaporation, and sputtering. A patterning operation may contribute to the removal of selected portions of one or more layers formed by layering. A doping operation may place dopant atoms upon and within exposed surfaces of the semiconductor wafers, thereby producing the p-n junctions required for semiconductor operation. A heat treatment may heat the one or more semiconductor wafers to achieve specific results (e.g., dopant drive-in or annealing).
Each wafer fabrication tool typically performs a wafer fabrication operation according to a predefined procedure (i.e., a predetermined set of steps or xe2x80x9crecipexe2x80x9d). For example, a given CVD wafer fabrication tool may carry out a layering operation within a chamber according to a recipe which specifies temperatures and pressures within the chamber as a function of time, as well as the types and flow rates of gases introduced into the chamber.
Characteristics of key integrated-circuit structures formed by wafer fabrication operations (e.g., gate oxide thicknesses) are typically measured to ensure the characteristics remain within acceptable ranges. In order to detect manufacturing problems as quickly as possible, such measurements are typically performed immediately following structure formations. Special test structures may be formed on test wafers processed along with xe2x80x9cproductxe2x80x9d wafers, or within test areas of product wafers, and the characteristics of the special test structures may be measured. Alternately, the characteristics of operational circuit structures formed upon product wafers may be measured. One common technique for tracking and analyzing manufacturing process variation is called statistical process control (SPC). SPC is typically used to gauge the stability of a manufacturing process over time via control charts which document historical process performance.
FIG. 1 is a diagram illustrating a current method for obtaining and documenting measurement data within a wafer fabrication facility. In a first step, an operator 10 submits the one or more wafers of the lot to a measurement tool 12 and selects a measurement recipe stored within measurement tool 12. Measurement tool 12 performs at least one measurement upon the wafers of the lot according to the selected recipe and displays the resulting measurement data upon a display screen (not shown). Operator 10 then manually enters the displayed measurement data into a log book 14.
In a second step, operator 10 carries log book 14 to a computer terminal 16 connected to a work-in-process (WIP) server 18. WIP server 18 tracks lots, schedules wafer processing operations, and stores measurement data. Operator 10 manually enters the measurement data via a keyboard of computer terminal 16, and computer terminal 16 transfers the measurement data to WIP server 18.
In a third step, operator 10 carries log book 14 to a stand-alone SPC computer 20. SPC computer 20 performs statistical operations upon input measurement data and plots the resulting statistical data on one or more control charts. Operator 10 manually enters the measurement data via a keyboard of SPC computer 20 and views the control charts to ensure the plotted statistical data lies within acceptable ranges.
The current method for obtaining and documenting measurement data described above is time consuming and error prone. Operator 10 may submit an incorrect lot to measurement tool 12, resulting in erroneous measurement data. Operator 10 may select an incorrect measurement recipe, again resulting in erroneous measurement data. Operator 10 may make an error when manually entering the measurement data into log book 14, similarly resulting in erroneous measurement data. Operator 10 must physically carry log book 14 to computer terminal 16 and to SPC computer 20. Operator 10 may make an error when manually entering the measurement data via the keyboard of computer terminal 16 or SPC computer 20, again resulting in erroneous measurement data. It would thus be desirable to have an automated method for obtaining and documenting measurement data within a wafer fabrication facility.
The problems outlined above are in large part solved by a wafer fabrication system including a measurement system which screens measurement data prior to dissemination. The measurement system may include an equipment interface computer coupled between a measurement tool and a work-in-process (WIP) server. The measurement tool may perform one of possibly several measurement procedures (i.e., xe2x80x9crecipesxe2x80x9d) upon one or more semiconductor wafers processed as a lot, thereby producing measurement data. The WIP server may select the measurement recipe and store the measurement data. The equipment interface computer may receive the measurement data produced by the measurement tool and compare the measurement data to a predetermined range of acceptable values in order to determine if the measurement data is within the range of acceptable values. The equipment interface computer may display the measurement data upon a display device such that any portion of the measurement data not within the range of acceptable values is visually flagged (e.g., displayed in flashing type, in bold type, in a color which differs from surrounding text, with a background color which differs from surrounding text, etc.). The equipment interface computer may allow an operator to modify at least the portion of the measurement data not within the range of acceptable values, then generate a signal indicating acceptance of the measurement data. Upon receiving the signal indicating acceptance, the equipment interface computer may provide the measurement data to the WIP server. The equipment interface computer may also respond to the acceptance signal by providing the measurement data to an entity server and/or a statistical process control (SPC) server.
The measurement system may also include a switch coupled between the measurement tool and the equipment interface computer. In a first position, the switch may couple the display device and a keyboard to the equipment interface computer. In a second position, the switch may couple the display device and the keyboard to the measurement tool. When the switch is in the first position, the equipment interface computer may receive substitute measurement data and the signal indicating acceptance from the keyboard. The equipment interface computer may replace the measurement data produced by the measurement tool with the substitute measurement data received from the keyboard.
The substitute measurement data may be generated by causing the measurement tool to repeat the measurement recipe or to perform a different measurement recipe. The operator may generate substitute data by placing the switch in the second position and entering measurement recipe selection information via the keyboard. The measurement tool may respond to the measurement recipe selection information by performing the specified measurement recipe upon one or more of the semiconductor wafers of the lot and providing the resulting (i.e., substitute) measurement data to the display device via the switch. The operator may then place the switch in the first position and enter the substitute measurement data via the keyboard. With the switch in the first position, the equipment interface computer may receive the substitute measurement data from the keyboard and replace the original measurement data with the substitute measurement data.
When the operator is ready to accept the measurement data as displayed upon the display device, the operator may press one or more predetermined keys of the keyboard. The pressing of the one or more predetermined keys may result in a signal indicating acceptance of the measurement data. The equipment interface computer may receive the signal indicating acceptance via the switch and respond by providing the measurement data as described above.
The measurement system may also include a keyboard interface coupled between the keyboard and the switch, and a bar code reader coupled to the keyboard interface. The keyboard interface may couple both the keyboard and the bar code reader to the switch. The bar code reader may be used to identify the wafer lot via an alphanumeric code printed in a bar code format upon a xe2x80x9crunxe2x80x9d card which accompanies the lot. The bar code reader may read the bar code thereby producing bar code information. When the switch is in the first position, the equipment interface computer may receive the bar code information via the keyboard interface and the switch. The equipment interface computer may provide the bar code information to the WIP server, and the WIP server may respond to the bar code information by providing lot information and measurement recipe selection information to the equipment interface computer. The equipment interface computer may provide the measurement recipe selection information to the measurement tool. The measurement tool may respond to the measurement recipe selection information by performing the measurement recipe upon one or more semiconductor wafers of the lot.
The wafer fabrication system may also include a process tool coupled to a workstation controller. The process tool may perform a wafer fabrication process (e.g., a layering operation, a patterning operation, a doping operation, or a heat treatment) upon the one or more semiconductor wafers of the lot. The process tool may operate in response to control signals received from the workstation controller. The workstation controller, equipment interface computer, and WIP server may be connected to a common transmission medium (e.g., a twisted-pair cable, a coaxial cable, etc.). In addition to storing measurement data, the WIP server may schedule the process performed by the process tool.
A method for screening measurement data in accordance with the present invention includes receiving the measurement data and determining if the measurement data is within a range of acceptable values. A portion of the measurement data not within the range of acceptable values is flagged, and at least the flagged portion of the measurement data is made accessible for modification. The measurement data is provided to a data storage device only after a signal indicating acceptance of the measurement data is received. As a result, out-of-range measurement data is prevented from being provided to the data storage device without review and acceptance.